The present invention relates to air tubes for use with spirometers, and to spirometers using such air tubes. More particularly, the present invention relates to air tubes which are disposable and at least partially biodegradable, and to spirometers, preferably differential pressure spirometers, which employ such air tubes.
Spirometers are devices used to measure the volume and flow rate of gas exhaled by a user or patient, for example, a human being. These measurements are important for physiological studies and for diagnostic analysis of the pulmonary performance of the spirometer user. For example, the effects of various medicines used to treat patients with pulmonary or asthmatic problems can be analyzed by monitoring the volume and flow rate of gas exhaled before and after the administration of medication. Several devices are available on the market which are known as pneumotachs, such as the Fleisch Pneumotach. These devices depend on a laminar air flow past a resistance element. Other spirometers employ more sophisticated electronics so that laminar flow is not needed.
Measuring the pressure difference or differential pressure of exhaled gas across an element which creates or causes the pressure difference is the basis for differential pressure spirometers. In such differential pressure spirometers, it is important that the air tube (pneumotach) be precisely configured and positioned, for example, relative to the pressure sensing and electronics systems of the spirometers so that measurements can be reliably and reproducably made. Such precisely configured pneumotachs, rather than being disposable, are made out of metals or durable plastics to be long lasting and effective after many uses without structural degradation. See, for example, Waterson et al U.S. Pat. No. 5,137,026, the disclosure of which is hereby incorporated in its entirety by reference herein.
Since most spirometers involve passing exhaled gas directly from the respiratory system of a user into the instrument for measuring, one important complication of using such devices is contamination from one patient to another patient if the same spirometer is employed by both.
Various approaches to overcoming this contamination problem have been suggested. A particularly popular approach is to use a disposable mouthpiece and filter over the inlet to the spirometer. The patient using the spirometer comes in contact only with the mouthpiece and is able, at least in theory, to avoid contaminating the remainder of the device. Drawbacks to this approach include the relative expense of such mouthpieces/filters, and the relative inefficiency of such systems.
Another approach to overcoming this contamination problem is to sterilize the portion or portions of the spirometer which come in contact with the user and/or exhaled air. Drawbacks to this approach include having to spend additional capital on sterilization equipment, having to monitor the operation and efficacy of the sterilization equipment, and having to purchase relatively durable and expensive spirometers to withstand the sterilization procedures.
A third alternative that has been suggested is the use of disposable spirometer components. See, for example, Norlien et al U.S. Pat. No. 5,038,773; Acorn et al U.S. Pat. No. 5,305,762; Karpowicz U.S. Pat. No. Des. 272,184; Boehringer et al U.S. Pat. No. 4,807,641; and Bieganski et al U.S. Pat. No. 4,905,709. Such previous disposable spirometer components have been made out of durable plastics or medical grade metals so that, even though they are disposable, the cost of producing such components is relatively high. In addition, such disposable components are relatively difficult to dispose of, for example, because they are made of durable and long lasting materials.
It would be advantageous to provide spirometers and spirometer components which avoid cross-patient contamination and which can be economically, conveniently and effectively produced and used.